Why do the Japanese judge by season, not by temperature?

I was in the park with my daughter the other day on a fairly chilly evening and noticed that she was the only one with long sleeves on. That shouldn’t have surprised me, what with salarymen changing to short sleeved shirts all on the same day (even before “cool biz” came along) and swimming in most of Japan stopping on 31 August whatever the weather on 1 September, but it did make me ponder the matter again.

You hear a lot that the Japanese are obsessed with seasons and nature generally, and if you look at the street decorations, elementary school syllabuses, advertising, and changes in kimono during the year, that does seem to be true. Ditto for the big fuss about new rice and the best seasons for fish. Frankly, though, I think it is more to do with not wanting to stand out, and been put through the excessive reactions to stories of me swimming in September I can quite understand why anyone Japanese would want to avoid doing anything that causes comment…